Fugacity vs. Fugacity Coefficient

Attribute	Fugacity	Fugacity Coefficient
Definition	The escaping tendency of a component from a non-ideal mixture or phase	A dimensionless quantity that relates the fugacity of a component in a mixture to its partial pressure
Symbol	f	φ
Units	Pressure units (e.g. atm)	Dimensionless
Dependence on Pressure	Depends on pressure and temperature	Depends on pressure and temperature
Calculation	Calculated using fugacity coefficient and partial pressure	Calculated using activity coefficient and partial pressure

Fugacity and fugacity coefficient are two important concepts in thermodynamics that are used to describe the behavior of gases and other substances. While they are related, they have distinct attributes that set them apart. In this article, we will explore the differences between fugacity and fugacity coefficient and how they are used in thermodynamics.

Definition of Fugacity

Fugacity is a measure of the escaping tendency of a substance from a non-ideal gas or liquid mixture. It is defined as the hypothetical partial pressure of a substance in a mixture that would be required to replace the actual partial pressure of the substance, while keeping the temperature and volume constant. Fugacity takes into account the non-ideal behavior of gases and liquids, unlike partial pressure, which assumes ideal behavior.

Definition of Fugacity Coefficient

The fugacity coefficient is a dimensionless quantity that is used to correct for the non-ideality of gases and liquids in thermodynamic calculations. It is defined as the ratio of the fugacity of a substance to its ideal gas or liquid partial pressure at the same temperature and volume. The fugacity coefficient accounts for deviations from ideal behavior and is used to adjust thermodynamic calculations to more accurately reflect real-world conditions.

Relationship between Fugacity and Fugacity Coefficient

While fugacity and fugacity coefficient are related concepts, they serve different purposes in thermodynamics. Fugacity is a measure of the escaping tendency of a substance from a mixture, while the fugacity coefficient is a correction factor that accounts for non-ideality. In other words, fugacity is a property of the substance itself, while the fugacity coefficient is a property of the system in which the substance is present.

Calculation of Fugacity and Fugacity Coefficient

The calculation of fugacity and fugacity coefficient involves complex thermodynamic equations that take into account the non-ideal behavior of gases and liquids. Fugacity can be calculated using equations such as the virial equation of state or the Peng-Robinson equation, which account for interactions between molecules. The fugacity coefficient is typically calculated using empirical correlations or experimental data.

Applications of Fugacity and Fugacity Coefficient

Fugacity and fugacity coefficient are used in a wide range of applications in thermodynamics and chemical engineering. They are commonly used in the design of chemical processes, such as distillation and absorption, where accurate predictions of gas and liquid behavior are essential. Fugacity and fugacity coefficient are also used in environmental engineering to model the behavior of pollutants in air and water.

Conclusion

In conclusion, fugacity and fugacity coefficient are important concepts in thermodynamics that are used to describe the behavior of gases and liquids in non-ideal conditions. While fugacity measures the escaping tendency of a substance from a mixture, the fugacity coefficient corrects for non-ideality and accounts for deviations from ideal behavior. Both fugacity and fugacity coefficient play a crucial role in thermodynamic calculations and are essential for accurate predictions of gas and liquid behavior in a wide range of applications.